Valor (corrigez-moi svp)

[north horizon]

Please be patient

Our volunteers look into many questions every day; sometimes it takes them a little while to answer.

Pro tip: you can rename the thread title with `.tr <thread name>`

Make it descriptive, including relevant context, but also to the point. This way you improve your chances of getting a more relevant and specific answer.

[viral bobcat]

It's the lack of 'des' that's incorrect.

Ils sont des photographes célèbres.
This should work too.

[modern gale]

If there were no adjective after photographe, you could go with either "Ils sont photographes" or "Ce sont des photographes"

However, it seems the presence of the adjective prevents the use of the former syntax.

What I think happens here is that when you say "Ils sont photographes", photographes is treated as an adjective, hence the absence of an indefinite article and the use of ils sont as opposed to ce sont.

But when you add another adjective, then it's no 'longer possible to treat photographe as an adjective because adjectives can't modify other adjectives

A similar phenomenon is found in colors (though it is purely orthographical and not a rule embedded in the language itself) :
When you say "des voitures bleues", bleues agrees in gender/number with voitures. However, if you add a modifier like in "bleu clair", the whole thing becomes invariable : des voitures bleu clair

The reason for that is seemingly the same: clair is an adjective that modifies bleu, forcing bleu to no longer be an adjective and instead be the masculine noun "bleu" referring to the color blue.

[viral bobcat]

(Unless the colour is also a noun, like 'marron' or 'orange'. Then it doesn't change, but that's a topic for a different thread.)

Des voitures bleues.
Des voitures orange.

[crimson glade]

I think they may be missing the main issue:
Ils sont + adjective
Ce sont + noun

Based on this, as Nired said:
Ils sont photographes
Ce sont des photographes

Ce sont des photographes célèbres ("célèbres" forcing photographes to be a noun as an adjective can't modify another adjective)

[minor sonnet]

apologies for not replying I was asleep

I thought that you don't use articles when saying a profession? Like "je suis étudiant". So why is the des required here?

Duo did accept it with the des included, which is nice. I keep forgetting these small things mdr

[crimson glade]

Because without an article, it acts as an adjective
Adjectives cannot modify adjectives, so modifying it with an adjective forces it to only be a noun, thus requiring an article

[crimson glade]

.

[minor sonnet]

Oh, huh. Didn't realize it was treated as an adjective normally.

[crimson glade]

Yea

That's also why you can use "ils" with them